During the refining process, hydrocarbon streams are frequently exposed to elevated temperatures, which can lead to premature polymerization of the desired monomer. The premature polymerization results in reduction of the amount of the desired monomer end-products as well as a loss in efficiency caused by fouling and deposit formation within the processing equipment.
In order to reduce or prevent polymer formation, stabilizing or inhibitor compositions have been introduced into the hydrocarbon stream at or upstream of a location where polymerization is likely to occur, such as where distillation is performed.
Phenylenediamines (PDA's) are widely used as antioxidants and polymerization inhibitors. However, their use is limited to hydrocarbon streams where the PDA is soluble. A number of patents relate to the use of various PDA's, combinations of different PDA's and combinations of PDA's with other inhibitors to stabilize hydrocarbon fluids.
Among these patents is U.S. Pat. No. 6,200,461 to Eldin which describes methods and compositions for inhibiting the polymerization of ethylenically unsaturated hydrocarbons under both processing and storage conditions by the addition of combinations of aminophenol compounds and either PDA or hydroxylamine. Other combinations have also been used. These include inhibitor combinations containing a PDA with an oxime compound and a hydroxylamine as shown in U.S. Pat. No. 5,489,718 to Arhancet. Other examples include the combination of a PDA and a hydroxylamine as shown in U.S. Pat. No. 5,396,004 to Arhancet and a PDA with a hydroxytoluene compound as shown in U.S. Pat. No. 5,416,258 to Arhancet et al.
Examples of specific PDA compounds may be found in U.S. Pat. No. 4,929,778 to Roling which describes compositions including a PDA compound which has at least one N—H bond and a hindered phenol useful for inhibiting the polymerization of styrene during elevated temperature processing, storage and shipment. U.S. Pat. No. 4,774,374 to Abruscato et al. discloses an oxygenated species formed by the reaction of oxygen and an N-aryl-N′-alkyl-p-phenylenediamine.
While each of these references provides compositions and methods that reduce premature polymerization of ethylenically unsaturated monomers, they are generally limited to hydrocarbon processing and storage where they are soluble, which does not include where water is present. Therefore, the currently available PDA inhibitors do not adequately address the concerns of the prevention of premature polymerization of a monomers with water-solubility, where a water phase is present.
Therefore, it would be desirable to provide a water-soluble composition for the reducing and or preventing the polymerization of ethylenically unsaturated monomers. Desirably, the composition will include a water-soluble phenylenediamine composition which acts as an antioxidant/free-radical polymerization inhibitor.